The proposed study will elucidate regulatory controls in the replication of mitochondrial DNA; replicative forms will be isolated from thymidine kinase minus lines of mouse cells. Control of replication at the level of transcription will be examined through the use of Dark-field Electron Microscopy of purified transcription complexes and by density gradient centrifugation of pulse-labeled components. Mitochondrial DNA replication will be stimulated by release of the tissue culture cells from stationary growth or infection with oncogenic viruses. Transcriptional control through RNA priming and regulation mediated through mitochondrial specific DNA nucleases will be examined. Physical mapping of control elements on the mitochondrial genome will be performed by electrophoresis and electron microscopy of restriction endonuclease fragments. Parallel studies will be conducted with circular dimer mitochondrial forms purified from human leukemic white cells before and after patients have been treated with antileukemic drugs. Control at initiation of displacement replication and the general validity of the displacement loop model for mitochondrial DNA replication will be tested through labeling studies and electron microscopy of replicative forms. BIBLIOGRAPHIC REFERENCES: Monahan, J.J., Harris, S.E., Woo, S.L.C., Robberson, D.L., and O'Malley, B.W. (1976): "The Synthesis and Properties of the Complete Complementary DNA Transcript of Ovalbumin mRNA." Biochemistry 15: 223-233. Robberson, D.L., Wilkins, C.E., Clyton, D.A., and Doda, J.D. (1977): "Microheterogeneity Detected in Circular Dimer Mitochondrial DNA.", Nucleic Acids research, in press.